Oil and gas wells (wellbores) are usually drilled with a drill string that includes a tubular member having a drilling assembly (also referred to as the bottom hole assembly or “BHA”) with a drill bit attached to the bottom end thereof. The drill bit is rotated to disintegrate the earth formations thus drilling the wellbore. The BHA includes devices and sensors for providing information about a variety of parameters relating to the drilling operations, behavior of the BHA and formation surrounding the wellbore being drilled (formation parameters). A variety of sensors, including radiation detectors, generally referred to as logging-while-drilling (LWD) sensors or measurements-while-drilling (MWD) sensors, are disposed in the BHA for estimating properties of the formation. Radiation sensors, whether for detecting gamma rays naturally occurring in the earth (passive measurement) or radiation emitted in the formation in response to induced radiation from a radiation source (“active measurement”), are placed in the BHA. Such sensors are close to the formation and may provide high resolution results relating to distinguishing rock formations when the drill bit moves from one type of formation to another, such as from shale to sand or vice versa. However, these sensors are placed far from the bit above the mud motor and thus they cannot provide information relating to the formation near or at the drill bit.
Therefore, there is a need for systems that allow for placing sensors close to the drill bit for improved estimations of formation properties during drilling of a wellbore.